"It goes against you sometimes; it goes for you sometimes," Isner said. "It's unfortunate, but I'm not going to dwell on it. He was better than me today."
Federer recalled winning a match the same way against Ivan Ljubicic in a Key Biscayne final.

"I actually texted him to tell him the same thing happened again," Federer said with a chuckle.

"Maybe I just got really lucky today," he said. "But overall I felt I played a great match. ... I think I'm playing my best. I don't know if you can play a whole lot better."

Federer needs one more win to clinch the first singles medal of his career.

"Being in the medal matches, at least I'll get two shots," Federer said. "That's why I looked at this match as a final. You can imagine the relief and happiness I feel right now."

On facing del Potro next, Federer said, “I’m not surprised he’s made it to the semis. He’s played a lot of tennis this year. I think he took advantage of the draw here and then was able to come through convincingly. I have my hands full with Juan Martin. He’s a big player with a big serve. That makes it obviously tricky on a fast court like grass.”

Delpo started better by taking the lead but then allowed Nishikori to levelled at 2-2. The Argentine broke again in the eighth game and even he got some troubles closing the set he finally did it..

In the second set, del Potro served for the match at 5-3 but double-faulted to hand Nishikori the break of serve.

The Japanese then held to send the set into the tie-break, which del Potro won to wrapped up victory in one hour and 55 minutes.